如何保存和重新显示 InstanceState

Question

我开发了一个应用程序，用户可以在一个屏幕上成组扫描一些条形码——一组可能有 2 个，另一组可能有 3 或 4 个。这些条形码相距很远，例如。一组中的第一个可能在建筑物的前面，然后其他人在建筑物的后面，等等。有时他们在完成建筑物之前被叫到另一个站点，并且必须移动到同一应用程序中的另一个屏幕并在那里做点什么。当他们返回扫描到一半的建筑物并重新显示原始屏幕时，他们希望重新显示该组中已经完成的扫描，因此他们只需完成该组即可。 我看过“protected override void OnSaveInstanceState(Bundle savedInstanceState)”所以当他们改变屏幕时，这段代码运行：

        protected override void OnSaveInstanceState(Bundle savedInstanceState)
    {
        savedInstanceState.PutString("gstrThisSiteID", gstrThisSiteID);
        savedInstanceState.PutString("gstrThisSiteName", gstrThisSiteName);
        savedInstanceState.PutString("gstrThisSiteNameFromUnfinishedSiteScan", gstrThisSiteNameFromUnfinishedSiteScan);
        savedInstanceState.PutString("gstrListOfScansDoneForThisSiteAdd", gstrListOfScansDoneForThisSiteAdd);
        savedInstanceState.PutString("gstrListOfScansForThisSiteRemove", gstrListOfScansForThisSiteRemove);
        savedInstanceState.PutString("gstrThisTagIDOrBarCodeValue", gstrThisTagIDOrBarCodeValue);

        //Always call the base implementation
        base.OnSaveInstanceState(savedInstanceState);

        Toast.MakeText(this, "OnSaveInstanceState(Bundle savedInstanceState)", ToastLength.Long).Show();

    }

这似乎运行正常 - 吐司按预期弹出。 但是，当用户返回条码扫描屏幕时，这些值不会重新出现。这是我的代码：

            if (savedInstanceState != null)
        {
            //_counter = bundle.GetInt("click_count", 0);

            Toast.MakeText(this, "savedInstanceState != null", ToastLength.Long).Show();

            gstrThisSiteID = savedInstanceState.GetString("gstrThisSiteID", "");
            gstrThisSiteName = savedInstanceState.GetString("gstrThisSiteName", "");
            gstrThisSiteNameFromUnfinishedSiteScan = savedInstanceState.GetString("gstrThisSiteNameFromUnfinishedSiteScan", "");
            gstrListOfScansDoneForThisSiteAdd = savedInstanceState.GetString("gstrListOfScansDoneForThisSiteAdd", "");
            gstrListOfScansForThisSiteRemove = savedInstanceState.GetString("gstrListOfScansForThisSiteRemove", "");
            gstrThisTagIDOrBarCodeValue = savedInstanceState.GetString("gstrThisTagIDOrBarCodeValue", "");

            CPsWaitingTextView = FindViewById<TextView>(Resource.Id.CPsWaitingTextView_id);
            CPsWaitingTextView.SetTextSize(Android.Util.ComplexUnitType.Dip, (float)20);
            CPsWaitingTextView.SetTextColor(Android.Graphics.Color.White);
            CPsWaitingTextView.Text = "strCheckpointsForThisSite";
            CPsWaitingTextView.MovementMethod = new Android.Text.Method.ScrollingMovementMethod();

            CPsScannedTextView = FindViewById<TextView>(Resource.Id.CPsScannedTextView_id);
            CPsScannedTextView.Text = gstrThisSiteName;

        }
        else
        {
            Toast.MakeText(this, "savedInstanceState IS null", ToastLength.Long).Show();

        }

在我开发应用程序时，当我返回到条形码屏幕时，toast 显示“savedInstanceState IS null”并且两个 TextView 未显示预期值。 我已将“if (savedInstanceState != null)”块放在 OnCreate void 的脚下：

        protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.TagAndBarcodeLayout);

        //Many lines of code setting up the screen etc, etc.
        //.............

        if (savedInstanceState != null)
        {
            //_counter = bundle.GetInt("click_count", 0);

            Toast.MakeText(this, "savedInstanceState != null", ToastLength.Long).Show();

            gstrThisSiteID = savedInstanceState.GetString("gstrThisSiteID", "");
            gstrThisSiteName = savedInstanceState.GetString("gstrThisSiteName", "");
            gstrThisSiteNameFromUnfinishedSiteScan = savedInstanceState.GetString("gstrThisSiteNameFromUnfinishedSiteScan", "");
            gstrListOfScansDoneForThisSiteAdd = savedInstanceState.GetString("gstrListOfScansDoneForThisSiteAdd", "");
            gstrListOfScansForThisSiteRemove = savedInstanceState.GetString("gstrListOfScansForThisSiteRemove", "");
            gstrThisTagIDOrBarCodeValue = savedInstanceState.GetString("gstrThisTagIDOrBarCodeValue", "");

            CPsWaitingTextView = FindViewById<TextView>(Resource.Id.CPsWaitingTextView_id);
            CPsWaitingTextView.SetTextSize(Android.Util.ComplexUnitType.Dip, (float)20);
            CPsWaitingTextView.SetTextColor(Android.Graphics.Color.White);
            CPsWaitingTextView.Text = "strCheckpointsForThisSite";
            CPsWaitingTextView.MovementMethod = new Android.Text.Method.ScrollingMovementMethod();

            CPsScannedTextView = FindViewById<TextView>(Resource.Id.CPsScannedTextView_id);
            CPsScannedTextView.Text = gstrThisSiteName;

        }
        else
        {
            Toast.MakeText(this, "savedInstanceState IS null", ToastLength.Long).Show();

        }

我是否将“if (savedInstanceState != null)”块放在了错误的位置？如果是应该去哪里？我还错过了什么吗？

提前谢谢你。